From a specified time in the past.
"I have lived here since 2015."
In plain English: Since means starting from a specific time and continuing up to now.
"I have been working here since morning."
From: referring to a period of time ending in the present and defining it by the point in time at which it started, or the period in which its starting point occurred.
"She has lived in London since 2015."
Continuously during that period of time.
"The engine has been running since morning without stopping."
From the time that.
"Since I arrived at the station, I have been waiting for my train."
Since comes from Middle English syns, a contraction of earlier forms meaning "after" or "since." This word traces back to Old English phrases that literally meant "after that time," combining words for "since" and "that."